The present invention relates to diagnosing failures and potential failures in electric motor driven systems and more particularly in electric motor driven pumping systems such as wastewater lift stations.
Wastewater lift stations (WWLS) are found in virtually all sewer systems. They serve to lift wastewater from low elevations along the sewer line to higher elevations so as to maintain a continuous down-slope grade to the receiving wastewater treatment facility. Failure of a WWLS can result in substantial environmental damage, and/or property damage when wastewater is discharged from the sewer line or floods residential or commercial drains. To avoid such events, sewer system operators employ various methods of monitoring WWLS""s to detect component failures or degradation so that maintenance action can be taken before damage occurs.
One method commonly used is to conduct periodic manual inspections. The inspection period can range from one or more inspections per day to weekly inspections. In any case, manual inspections involve travel to each WWLS, and since most WWLS""s are constructed below the ground surface, special precautions must be observed to safely enter the station. A common problem with intermittent manual inspections is that they fail to diagnose signs of failure that may appear between inspections, and they often lack sensing devices that can detect failure symptoms before they can be observed manually. Furthermore, by the time a failure symptom can be observed manually, significant damage to the station may have occurred.
Another method is to install an automated monitoring or control system designed to detect and report failures of station components early enough to allow corrective actions that may prevent or minimize damage. For example, as disclosed by Irwin (U.S. Pat. No. 6,178,393 B1) a drop in pump efficiency, as determined by the energy use compared to its output, may indicate a problem with a pump, thus triggering a preventative action prior to a catastrophic failure. Another measure of efficiency in common use is the wire-to-water efficiency as an indicator of the health of the pumping system.
A critical factor in the diagnosis of pumping systems is the cost of the diagnostic system. To justify the installation of a diagnostic system, the savings over the life of the system must substantially exceed its cost. Savings accrue in proportion to failure rates and the economic consequences of a failure. Failures can be classified in a range of events from a slight degradation of performance to a complete breakdown of pumping function. Most pumping systems employ a means of detecting complete breakdowns, but small degradations may go undetected for long periods of time before being discovered. Nevertheless, small degradations over a long period can add up to large costs. Also, degradations of a certain type can quickly grow to a complete breakdown if not corrected promptly. Therefore another important consideration in the diagnosis of pumping systems is the identification of the kind of problem that is developing. For example, detection of an obstruction in the discharge or inlet pipe would demand more immediate attention than detection of a worn pump impeller. In the case of an obstruction, the maintenance crew can be dispatched with the tools needed to correct a plugged line, whereas, in the case of a worn pump impeller, the replacement operation can be scheduled far in advance with the proper replacement parts in hand before a maintenance crew is dispatched. To arrive at a site and discover a problem that requires tools or parts that are not immediately available adds costs and time to the repair operation. Alternatively, having to carry an inventory of expensive tools and parts to every maintenance event because of a lack of knowledge about the cause of problem that will be encountered is costly. Current, low cost, diagnostic systems fail to provide definitive information about the cause of failures.
Early detection is a very important aspect of pump system diagnostics. In general, other low cost systems only detect failures after they have reached a critical stage such as high water level alarms. Once the pump system has failed to the point that the pumps are no longer able to keep up with the inflow into the site, repair crews have a very limited amount of time to travel to the site and fix the problem before backups occur. Backups are instances where raw sewage pools in the sewer lines because of a failure in the collection system, generally an obstruction in the lines or a failed pump. If the backup persists long enough, the sewage will begin to collect in the basements of homes and other low spots. Backups commonly cause extensive damage to residential neighborhoods and commercial areas; damage that municipalities are responsible for repairing. Being able to detect partial blockages and failing pumps early on in the failure cycle can save repair crews tremendous amounts in both labor and liability costs. With early detection, there is sufficient time to correct even the most difficult problems or arrange for other means of handling the sewage before a backup can occur. Early detection can also allow wastewater operators more leeway in scheduling repairs during normal working hours rather than on an emergency basis.
So, the most advantageous diagnostic systems are those with the lowest cost and the highest problem resolution capability. The three major cost elements of remote diagnostic systems relate to sensors, communication methods, and processors. Sensor costs vary in proportion to the number and type of sensors used in the diagnostic system. For example, Irwin (U.S. Pat. No. 6,178,393 B1) employs a power sensor and a flow sensor to derive just two operating variables (i.e. energy and volume pumped). Others use various combinations of sensors including amperage sensors, flow sensors, pressure sensors, level sensors, vibration sensors, temperature sensors, etc. Current disclosures require multiple sensory inputs to accomplish detailed diagnoses and fail to describe methods of automatically calculating such diagnoses. Sensors are typically connected to a remote processor, which converts the sensor signals to digital data representing various pump system parameters. Such data is then transmitted through communication systems to another processor where it is analyzed manually and the resulting diagnostic reports are made available to operators.
Typical practice for high-end monitoring systems is to transmit a large volume of data from each remote pump system to a central location where pump system operators may derive a diagnosis from examination of historical values of such data. Automation of the diagnostic process can substantially reduce communication requirements and labor time required for analysis of the data. Communication costs vary in proportion to the frequency and volume of the data transmitted. Examples of communication methods used in remote diagnostic systems include dedicated telephone lines, cellular telephones, cellular radios, and packet radios.
Processor costs vary in proportion to the number and capability of the processors. Remote diagnostic systems employ at least one processor at each remote site and usually more than one processor at the central facility overseeing the installation or set of installations (i.e. the lift stations managed by one municipality). The widespread availability of the Internet can reduce central site processing costs by servicing very large numbers of remote sites with a single web site facility that can distribute diagnostic reports anytime, anywhere through the Internet. However, while use of the Internet in remote diagnostic applications provides a means of reducing the processing cost elements, automatic methods that reduce sensor, communication and labor costs and increase problem resolution capability of diagnostic systems are still needed in order to economically provide diagnostic system benefits to most pumping systems.
Accordingly, the present invention is directed to a method and system for diagnosing potential pump system failure. A method embodying the invention includes calculating amperage variables for the pump motor using a signal from an amp sensor measuring electrical current used by the pump. Design values for the pump are acquired and diagnostic values are calculated using one or more calculated amperage variables and one or more of the acquired design values. Using the diagnostic values, diagnostic parameters are then calculated. Each design parameter is then compared with a baseline value or pattern. Where the design parameter verifies beyond a set tolerance limit, an adverse diagnosis is reported.